The Camera Obscura€¦ · The Camera Obscura: Its Uses, Action, and Construction p.3. One...

The Camera Obscura: Its Uses, Action, and Construction

by H. C. Standage

�An Except from Amateur Work Illustrated, Vol. IV, pages 67-71, 1885

This periodical for amateur craftsmen was published in London, England during the late 19th and early 20th centuries.

edited by the Author of Every Man His Own Mechanic

This article, from a bound volume of the periodical in our collection, has been scanned, processedwith optical character recognition, and corrected to the best of our ability. We can not guarantee theabsolute accuracy of the transcription since we are dealing with 19th century sentence style and worduse as well as the differences in English and American spelling.

The full page illustration that accompanies the article is reproduced on page 2 and the figures areinserted into the text for reference. Since important measurements correspond to letters on thediagrams we have also included an appendix with enlarged versions of each illustration to make theplacement of the key letters more readable.

The directions may appear wordy and convoluted to 21st century readers but should be detailedenough to be used or adapted by an experienced craftsman. We suggest that a prototype be made incardboard to test the function of the camera with your lens before committing to a final design.

This PDF can be printed and used without restriction and distributed if the credit line is included. Itshould not be reprinted without credit and can not be resold.

With best wishes for your success at camera obscura construction. If you are successful in building acamera obscura from these instruction please send us an email at [email protected] with apicture and. we will post it on our website.

Jack and Beverly Wilgushttp://brightbytes.com/cosite

Table of Contents (click on name or page number to jump to link to section)

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 1Page of illustrating figures . . . . . . . . . . . . . . . .page 2Text of article . . . . . . . . . . . . . . . . . . . . . . . . . .page 3 – 8Appendix of enlarged figures . . . . . . . . . . . . . .page 9 – 14Possible sources for optics . . . . . . . . . . . . . . . .page 15

�© 2004 Bright Bytes Studio page 1

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Note: Enlarged examples of these illustrations are found on pages 9 – 14.

The Camera Obscura: Its Uses, Action, and Construction p.2

THE CAMERA OBSCURA:ITS USES, ACTION, AND CONSTRUCTION:

By H. C. STANDAGE

HE use to which a camera obscura is now put is chiefly that of affording amusement tochildren. Such for instance, as the dark chamber at the Crystal Palace. Doubtless, all of my

readers are familiar with the picture depicted on the plaster table in the centre of this chamber, wherea tableau of all the objects in the Palace grounds is shown in their natural colour and motions. Butformerly this apparatus was used for drawing and photographic purposes. Its disuse for such purposesis chiefly due to better and vastly superior instruments; although, should anyone wish to trace anaccurate outline of a landscape on a miniature scale, the camera obscura holds its own, in the matterof convenience, against all comers.

There are several forms of apparatus, but the principles of their actionare the same in all instruments.

To easily comprehend the action of the camera obscura, it will bebetter to describe the principles which refer to any one form of theapparatus. Turning then to Fig. 1, we notice the following peculiarproperties. A is the wooden case or box for holding the lens B, of theshape shown in the figure. C is an opening in the side of this box; thisopening is for the purpose of allowing light rays from the distantlandscape to impinge on the convex surface of the mirror; while D isanother opening at the bottom of the box to allow these rays-which arereflected from the back of the lens, which is plane-to pass through thisopening on to the table or sheet of paper E, placed ready to receivethem. For the purpose of collecting these rays, so that they shall notscatter, but define the external landscape with distinctness, the bottomof the lens is concave, but with a larger radius of curvature than thefirst surface.

The box A may be square or cylindrical, and it can also be made to revolve horizontally. The insideof it should be blacked with lampblack, so that the full effect of the lens may be utilized by the lens.

The mirror B, in Fig. 1 is of a peculiar shape, andconsequently not always obtainable; in such cases thefollowing method (Fig. 2) of constructing the camerawill answer the same purpose, since the action isprecisely the same.

A, A, A, are the sides and top of the box holding thelens, C is the opening for the passage of the rays fromthe external landscape, while B is a plane mirror placedat an angle of 45˚ with the opening, and consequentlywith the convex lens F, which is fixed horizontally. Inthis construction we see that the rays strike directly on aplane surface, from which they are reflected, and passthrough a convex lens. This is the form of apparatus weshall adopt in the instrument we shall now describe howto construct.


One essential point, however, must be attended to in the construction of the camera, else theinstrument will not work satisfactorily. It is this, the drawing paper or table which is to receive theimage must be at a definite distance only from the lens, otherwise the picture represented will beblurred and confused. This distance is determined by the focal length,* as it is termed, of the lens. Agreater sharpness of outline is also obtained by having the receiving surface hollowed out to the samecurve as the lens; thus, the table at the Crystal Palace camera obscura is made of plaster of Paris,hollowed out to a concave form, the curvature being similar to the convexity of the lens.

(*To render this paper intelligible to those who know nothing of the principles of optics, I will explainthe meaning of this term presently.)

The simplest form of a camera may be made by fixing a convex lens in a hole in the window shutter.This lens should have a focal length of five or six feet, and at nearly half the focal length of the lensplace a looking-glass (ie., a plane mirror ; a sheet of ordinary glass covered on one side withlampblack will answer the same purpose, provided the unpainted side be turned towards the lens) at anangle of 45˚ with the axis of the lens. If then a sheet of paper, or a white cloth, be held at a distancefrom the looking-glass equal to the distance the latter is from the lens, an exact picture of the externallandscape and all the objects outside, whether in motion or not, will be represented on the paper orcloth. Every colour and movement of the animate objects will be seen as if the spectator were lookingat them direct. Note that the objects are in a reverse position to what they are in nature, unless thespectator looks at them with his back towards the lens in the shutter; to anyone in such a position they

will appear correct.

For greater distinctness the lens should be fixed in a tube a fewinches long, and the tube fastened into the shutter. Of course, nolight must enter the room except that coming through the lens.

There are two very good forms in which a portable CameraObscura for drawing purposes can be made, which I willproceed to describe.

With regard to the construction of the camera shown in Fig. 3,in order to make a cubic box measuring 9 inches every way onthe outside, plane up a piece of board 9 inches wide and 1/4inch thick, and then saw off five pieces, two of which are 9inches by 9 inches, or 9 inches square, which we will call B andC; one piece 9 inches by 8 1/2 inches, which we will call A;and two pieces 8 3/4 inches by 8 1/2 inches, which we will callD and E.

Take one of the pieces measuring 8 3/4 inches by 8 1/2 inches, and cut a circular hole in it, 2 inches indiameter; this hole is to receive the tube A containing the lens B. Next nail the five pieces togetherinto the form of a box. Since there are six sides to a box, we shall have one side open ; this open partis to cover the aperture in the larger box C.

To nail the nine pieces of wood together into box form proceed thus:– Nail the pieces B, and C (Fig.5), which are 9 inches square, to opposite edges of the piece A, which is 9 inches by 8 1/2 inches. Wenow have three surfaces of the box of equal areas, namely, 9 inches by 9 inches, because the breadthof A, namely 8 1/2 inches, is supplemented by the thickness of the sides B and C that are nailed to it,and thus brought up to 9 inches, because 8 1/2 inches + 1/4 inch + 1/4 inch = 9 inches. The pieces Dand E, which have been cut to the size, 8 3/4 inches by 8 1/2 inches, are now slipped in between the


boards that have been already nailed together, so that one of the short ends of each rests on A, the longends abutting against B and C, when it will be found that the edges of B, C, D, E, at the opening ofthe box, will be flush with each other. It is necessary to take care that they are exactly flush, in theconstruction of the camera, else, when this small box is secured to the larger one, it will not fit close,and consequently light will enter the apparatus.

When this box is made, place a plane mirror with the reflecting surface opposite to the circularaperture. This mirror is to be inclined to the side of the box where this circular aperture is, at an angleof 45˚. Since our box is cubical, the mirror will divide the box diagonally, as shown by the surfaceindicated by dotted diagonal lines in Fig. 5. To keep this mirror in its place, it should rest on a strip ofwood (about 1/8 inch thick), at the end E. This strip of wood is 8 1/2 inches long, and should be gluedin after the mirror is placed in position. The size of the mirror will be as nearly as possible 12 incheslong by 8 1/2 inches wide, the diagonal of a square (not of a cube) of 8 1/2 inches being very nearly12 inches. Remember the length of the mirror is only equal to the diagonal of one side (as C) of thecubical box (see Fig. 5).

The next proceeding is to construct the larger box C (Fig. 3). This has five sides, and is constructedafter the manner of that described in Fig. 5. The top, D, of Fig. 3, has a hole 8 1/2 inches square cutout, over which the smaller box is placed. This hole should be cut out of D previous to joining thesides together. The easiest way to cut out this square is to use a keyhole saw; thus, mark off on D, withpencil, the part to be cut out, then at each corner bore a hole with a gimlet large enough to let the endof the keyhole saw enter; insert the saw in one of these holes, and follow the pencil mark for one sideof the square to be cut out; when the next corner is reached, the gimlet hole will permit the saw beingreversed and follow the next pencil mark, ie., that at right angles to the first. Follow the other pencilmarks until the hole where the saw first entered is reached. This hole is half an inch less than the sizeof the small cubical box, so as to allow a foothold for the latter to rest on. The smaller box is securedto the top D by means of four angle brackets E; these brackets should be about 1 1/2 inch long in eachlimb and 1/2 inch wide, screws 3/8 inch long being used, care taken that the holes for them are notbored too deep nor penetrate through the wood.

The floor of the larger box forms the bed or table on which the sheet of drawing paper is laid. Theopen side of this larger box is covered with a cloth G, having a hole, H, for the operator’s head to passthrough, and another, I, for his arm. When the instrument is in position, the operator inserts his headthrough H and his right arm through I, and sketches off on the drawing paper the picture representedthereon. This cloth should be stretched across the box tight enough to exclude all light. On two sides,it should be nailed permanently to the box (say at the top and right side), while at the other sides it is

secured by eyelets in the edge of the cloth being fastened on to nails orhooks fastened on the sides of the box. This cloth or curtain is purposelymade to open so as to permit the insertion or removal of the drawing paper.A piece of baize or cloth impervious to light is the best to use. For thepurpose of focal adjustment the tube A should be double – that is, oneholding the lens should slide in an outer casing; This tube is best made ofsheet brass, with the joints soldered or brazed together; any tinman orsmith will make this tube for a trifling sum. Should the amateur desire toconstruct it himself, he must proceed thus :

Take a piece of sheet brass, or zinc (the latter will do equally as well), 7inches by 7 inches, and bend this over a wooden roller or piece of gas-pipe,or some other cylindrical article that is 1 7/8 inch in diameter. One edge


will overlap the other something less than an inch. This edge is then to be soldered. Next take a brasscurtain ring exactly 1 7/8 inch outside diameter, and solder this in one end of the tube. This ring is toprevent the lens falling out at this end of the tube. After this ring is soldered in, insert the convex lensfrom the other end of the tube, push it close up to this ring, and then put another one behind it. Thelatter one it is impossible to solder in, but the roughness of the inner part of the tube will not allow itto fall out easily. Make the soldered joint of the tube as thin and even as possible, else when it slidesin its outer casing a ray of light will penetrate into the box along side this joint. The outer tube isconstructed in the same manner as the first, the internal diameter of it being just equal to the externaldiameter of the inner tube. The sheet of metal of which this outer tube is made should be about 9inches long by 8 inches for bending into tube form. But across one end of the 9-inch length the metalshould be slit at intervals of about an inch (shown in Fig. 6, A), so that when the metal is bent intocylindrical form these slits will allow the metal to be bent back at right angles to the axis of the tube(as shown by B, Fig. 6). These flange pieces are for the purpose of fastening this outer tube to thesmaller box in Fig. 3, so as to cover the circular aperture therein.

Now comes one special point to attend to, and that is, the focal length of the lens. This “focal length”should be equal to the length of the dotted lines, X Y, Y Z – that is, it should be equal to the distancebetween the lens at Z to the mirror at Y, and from the mirror at Y to the bottom of the box at X. If thepictorial image at X is blurred, the tube holding the lens B should be adjusted (by drawing it out, orvice versa) until the image is distinct. Should the image then remain unsatisfactory, make a falsebottom on which to place the drawing paper. This is easily accomplished by putting a drawing boardor a smooth surface inside the box, andraising it to the required height by placingbooks or blocks of wood, etc., underneath.The plane mirror in the small box shouldbe distant from the lens B, not quite equalto half the focal length of the lens, while,at the same time, the sharpest picture willbe represented at a distance from thismirror at a like distance. The size of ourbox will take a lens having a focal lengthof 3 feet, when the most distinctlyoutlined picture will be represented at about 11 inches above the bottom of the box. By making, thetube A longer than the dimensions given, a lens of 3 feet 6 inches to 4 feet focus may be used; but inno case should the focal length be too great for the size of the apparatus – that is, the length shouldnot be so great as to depict the picture most distinctly below the bottom, as it were, of the larger box.

A few words of explanation of “focal length” will prevent all confusion in the minds of all such ashave no knowledge of optics. In, Fig. 7 I have represented a section of a double convex lens (such asis used in our camera); the line B, C, passing through the centre of the lens at right angles to itssurface, is called the principal axis of the lens. Now, when rays parallel to this principal axis passthrough a convex lens, the effect of the two refractions (refraction means bent or broken out of itscourse) which they undergo – one on entering, and the other on leaving the lens-is to make them allconverge approximately to one point, F, which is called the principal focus. The distance, A F, of theprincipal focus from the lens is called the principal focal distance, or more briefly and usually, thefocal length of the lens. Every school-boy, when be converges the rays of the sun on to the skin of hiswrists (for raising a blister, as some young rascals do, so that they shall be unable to do their writing


lessons), or to light a match or paper, knows the principal focus, for it is that point where the heat ismost intense, or the spot of light formed is the most minute. The focal length depends on the convexityof the surface of the lens. Consequently, a lens 1 7/8 inch diameter which is thicker in the middle than

another of the same diameter, will have a greater focallength than the latter. The focal length also depends on therefractive power of the material of which it is composed,being shortened either by an increase of refractive power,or by a diminution of the radii of curvature of the faces.

Another form of a camera obscura for drawing purposes isshown by Fig. 4. This form is perhaps the handier of thetwo. In this figure the box, A B, is cubical, and the focallength of the lens is equal to the distance F is from theside, A D E, of the box. By placing the mirror, D E G H atan angle of 45˚ to the axis of the mirror, the picture insteadof being depicted on the side, A D E, is reflected into thetop, D E K B. This top is formed of a sheet of glass groundon one side, the smooth side being undermost. On thisground surface, the landscape, etc., is represented in all its

natural colours. The objects represented can be drawn on the glass with a pencil, and afterwards copiedoff thus: Let this glass top be movable, then, when the picture is sketched on it in pencil, remove it,and lay it on a reflecting surface, such as a looking-glass, or brightly-polished sheet of metal. Then, ifa piece of tracing paper is laid on the Ground glass, the design will be rendered deep enough to betraced on the paper. If this paper be used, the design can be copied off the ground glass when the latteris in position in the camera.

In Fig. 4, B L M K is a lid, and B D L, K E M, side pieces that hinge on the box for the purpose ofexcluding extraneous light falling on the ground glass thus the picture represented thereon is rendereddoubly intense.

This last form of the camera obscura may be turned into a source of amusement, and will causeastonishment and wonder to anyone not acquaintedwith the construction of a camera. Thus, Fig. 8represents an ordinary table with a piece of the topcut out, and a sheet of ground glass let in in itsplace. The camera is fixed beneath the table asshown. The way to use it is as follows: Let thetable stand against the shutters when they areclosed, a large table-cover being placed on it, andfalling about its legs so as to hide the camera. Ahole must be made in the shutter just suitable toadmit the tube containing the lens (the lens needonly just cover this hole). When you wish toastonish the company present by telling them youcan show them all that is passing outside the housewithout the necessity of them leaving the room, allyou have to do is to place them round the table, darken the room, and withdraw the


table-cover. The company will be highly amused by the verification of your words, for on the tabletop will be represented a faithful picture of all external objects,

Instead of the external landscape, the doings of the party in an adjoining room can be shown to thecompany if the lens be placed against a hole cut in the folding- doors between the apartments. Thereare many other ways in which such a table can afford amusement to a company during the dull winterevenings. Thus, the following is suggestive of many others. Have two or three confederates, and letthem absent themselves from the company silently. After a short time commence operations byasking where they are, or if anyone knows what they are doing. When the excitement for theirappearance is eager, and some wish to go in search of the fugitives, offer to call in the aid ofspiritualism for their discovery. Some will doubt your ability to do so. So to verify your power, getthem to stand round the table (of course they can only stand round three sides of it), and take eachother’s hand. Darken the room, and then ask one of the company present which of the absentees it isdesired to know about. On her name being given, call for her in a loud voice, “Spirit of Alice, comeforth and show what Alice is doing.” At that moment pull away the cloth, and Alice will berepresented on the table top, either at needlework, dancing, skipping, etc. In a few seconds replacethe cover, and ask which other absentee shall appear, and repeat the question and operation.

Since the person will be represented on the table top in her natural colour and motions, extraordinaryastonishment will be caused, and almost a belief in your power of spiritual agencies. Of course, youmust have previously told the absentee confederates what to do, and whenever one is called (youmust call her name loud enough for her to hear it in the next compartment), the other absentees must place themselves out of the camera’s range. To produce greater mystery, so that the companyshall not recognize what room the absentees are in, let a screen or two form a background to theconfederate persons and their movements. A sliding top to the table instead of the cloth is a still better arrangement.


Fig. 1 Camera to Receive Image on Horizontal Table

Appendix of enlarged examples


Fig. 2 Camera Similar in Purpose to Fig.1 with Flat Mirror


Fig. 3 Portable Camera for Drawing Purposes


Fig. 4 Another Form of Portable Camera for Drawing Purposes


Fig. 5 Formation of Cubic Box for Camera


Fig. 7 Diagram Explaining Focal Length

Fig. 8 Ordinary Table Fitted with Camera


Possible sources for opticsWe have not purchased optics for any of the suppliers below except American Science &Surplus and Edmund Scientific, both of which we found very reliable. We can not give anyother endorsement or guarantee the availability of the websites.

Surplus optics are available from:

American Science & Surplus: http://www.sciplus.com/category.cfm?category=18Edmund Scientific: http://scientificsonline.com/category.asp?c=421191Sterling Resale Optic: http://sro-optics.com/Surplus Shed: http://www.surplusshack.com/Anchor Optical Surplus: http://www.anchoroptics.com/

High quality custom lenses for camera obscuras are available from:

*David Sindon: http://www.sinden.org.uk

* We know Sindon by reputation as the maker of the optical components of several veryimpressive camera obscuras we have visited. If you need and can afford very special lenseswe suggest you contact David Sindon.

©2004 Bright Bytes Studio

PDF prepared by Jack and Beverly Wilgushttp://brightbytes.com/cosite


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